<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>js变量函数预解析</title>
	<script type="text/javascript">    
    	aa();       // 弹出 hello！
   	 	alert(bb);  // 弹出 undefined
    	function aa(){
        alert('hello!');
    }
    	var bb = 123;
</script>
</head>
<body>
	
</body>
</html>